NMR Process Analyzer

Crude Oil Blending

The Crude Blending Application is an attractive solution for refineries with the ability to blend different crude types to provide a consistent and optimal feedstock to refinery operations.

Crude Blending Application is an intelligent blending operations control solution based upon Foxboro's extensive process knowledge and experience. This application solution includes the unique technology of our process NMR. The combination of a unique analyzer, advanced software and experienced engineering services enables Foxboro refinery customers to achieve business success

Operating the refinery at optimal and constant crude composition can generate savings for major refineries on the order of 2% to 3% of the operating margin of the whole refinery. The Crude Oil Blending solution achieves this by:

Improved distillation unit throughput. Constant attention to the distillation quality of the crude loads the crude distillation unit and all the other downstream units consistently. This allows refiners to operate their crude distillation unit closer to its limits, which increases throughput.
Improved higher value product yields. More stable and consistent operation allows operation closer to constraints. This enables the maximization of yields of higher value products.
Improved performance of downstream units. Specific characteristics of the crude will also influence performance of some of the downstream units. Changes in the ratio of paraffins to aromatics in crude, for example, will impact/affect the benzene, toluene, and xylene output of catalytic reformers.
Improved product quality and reduced energy costs. Stability of the crude composition also eliminates one of the major disturbance factors in a refinery, resulting in more stable operation. This contributes positively to overall quality, fosters efficient energy consumption, and improves equipment reliability.

NMR Application Details:

The process NMR component of the application for crude blending involves the correlation of NMR spectra to the following parameters:

API Gravity and Density
Water Content
True Boiling Point Values at ant temperature from C1 emission to 700^oC
Viscosity
Pour Point
Sulfur

Refinery Product Blending Systems

Advanced process control generally requires near real-time stream quality information. The exceptional availability of the NMR analyzer enables this information to be supplied reliably for process control, while the technology ensures accuracy and repeatability. Because this analyzer can be applied to numerous component quality measurements, a single analyzer can often alleviate the need for multiple analyzers to satisfy an APC or optimization application.

Foxboro's Blend Optimization and Supervisory System (BOSS) provides management of the component and product tanks, blend header, on-line and laboratory analytical systems, and planning/scheduling activities. BOSS produces blended products with a high degree of precision to meet specifications while minimizing quality giveaway. This maximizes the use of the lowest cost components in the blend, increasing the flexibility of the tank farm operation, and minimizing the frequency of reblends. A flexible objective function permits component cost, inventory constraints, or product specification to direct the optimizer.

The NMR analyzer provides BOSS with near real-time component stream and blended product chemical quality information. This information enables multivariable analyzer-directed control including:

Feedforward control for component quality variations
Feedback control for product quality variations
Quality integration of product and component tanks
Projected product qualities at the blend header

A refinery gasoline blending system upgrade project including blend optimization can provide benefits amounting to $0.15 to $0.30/bbl gasoline. Including the cost of engineering studies, new field equipment, and new instrumentation in a tank farm automation and blend optimization project, the payback period is typically less than 18 months. This is true for gasoline, diesel, and fuel oil blending operations.

Atmospheric Crude Oil Distillation

In the past, refiners would manage the transition from one crude to another by manual adjustment of various controlled variables for a given time, thus relying upon prior crude transition experience in order to minimize process upset.

By using NMR-enhanced control and process optimization, however, the refiner can follow the transition from one crude to another in real-time and proactively adjust parameters as needed to maintain maximized profit. The result can be dramatic savings per crude transition, since the typical 4-to-8 hour upset due to a transition is essentially eliminated.

ROMeo and Connoisseur maintain unit operation at optimum between crude transitions. Atmospheric tower overhead and sidecut product draw stream quality measurements provided by the Foxboro NMR are used in the Connoisseur model to monitor process operation performance and supply control feedback information. Common advanced control targets include:

Maximizing unit throughput up to equipment constraints
Maintaining product quality while maximizing yield of most valuable products
Optimized preheat train, pumparound, and fired heater operation

Including crude transition compensation and unit optimization, overall benefit can reach $0.12/bbl feed.

Fluid Catalytic Cracking

The fluid catalytic cracking unit (FCCU) is one of the most important units in the refinery. Few FCCUs have real-time process optimization implemented, since feeds typically have been measurable only in the laboratory. These measurements take many hours, with reports available only once or twice a day. Even the measurement of PIONA (paraffins, isoparaffins, olefins, naphthenes, and aromatics) and the distillation properties of the rundowns are difficult to achieve on-line.

The Foxboro I/A Series NMR now provides a means of obtaining these measurements near real-time, thus enabling significant economic benefit to the refiner through APC and process optimization.

FCCU controls and optimization include feed preparation, the reactor/regenerator, the main fractionator, the wet gas compressor, and the downstream gas plant. Typical operating objectives are

Maximizing unit capacity
Maintaining product quality while maximizing yields of most valuable products
Optimizing energy utilization
Controlling conversion
Improving safety and reliability via operational stability

Total economic benefit can approach $0.30/bbl feed.

In this application the process NMR unit provides control parameters based on the needs of the plant.

Different plants have different chemical and parameters of the FCC Feedstream to control or optimize the FCC unit.

Typical parameters requested for the NMR are:

Density
Sulphur **
Total Nitrogen **
Basic Nitrogen **
Metals ++
Micro Conradson Residue
Aniline Point
Refractive Index
Total Aromatics
Aromatic Breakdown (Mono, di, tri, tetra+ rings)
Distillation (D1160)
Viscosity
Hydrogen Content
Asphaltenes

** Secondary correlation

++Cannot be determined by NMR directly-Relaxation studies may allow quantification of Total Metals (No discernment between metal types).

All the above parameters can be modeled (except metals). Sulphur and nitrogen numbers will be secondary correlations that can be used only for gross estimation. These are poorer correlations because the NMR does not observe N or S directly, instead correlation is found in H chemistry that is elated to these heteroatoms. The remaining parameters can be modeled to an error of prediction somewhere between ASTM repeatability and reproducibility for the ASTM tests depending on the validation procedure that is followed.

Process NMR Associates is also developing large databases that correlate ¹H NMR spectra with ¹³C NMR parameters that are more useful and technically accurate than the above tests many of which simply correlate to the ¹³C NMR parameters of carbon aromaticity (F_A), carbon paraffinicity (F_P) and carbon naphthenicity (F_N). These parameters would be the preferred parameters for online control and optimization.

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Related Website: Process NMR Associates, LLC - Process analytical consulting company specializing in the application of nuclear magnetic resonance spectroscopy in on-line applications in the refining, petrochemical and food industries.